Inside the rambling, pale-yellow Colonial-style home in a Connecticut suburb, Adam Lanza lived amid a stockpile of disparate weaponry and macabre keepsakes: several firearms, more than 1,600 rounds of ammunition, 11 knives, a starter pistol, a bayonet, 3 samurai swords. He saved photographs of what appeared to be a corpse smeared in blood and covered in plastic, as well as a newspaper clipping that chronicled a vicious shooting at Northern Illinois University.

A gun safe was in what investigators believed was his bedroom. Among his clothing was a military-style uniform. There was also a holiday card that contained a check made out to Mr. Lanza, 20, and signed by his mother. Investigators suggested that the money had been intended to buy a gun.

The disturbing details of Mr. Lanza’s possessions were disclosed on Thursday for the first time since he carried out the massacre at Sandy Hook Elementary School in Newtown, Conn., one of the deadliest school shootings in the nation’s history. The information was included in search warrants and related affidavits connected to the investigation into the Dec. 14 attack, when he killed 20 first graders, 6 educators, his mother and himself.

The inventory of the house, combined with interviews conducted over several weeks with law-enforcement officials and people who crossed paths with the Lanza family, afford a somewhat fuller picture of the dark corners of Mr. Lanza’s mind.

The interviews revealed that his mother, Nancy Lanza, confided to friends several years ago that her son, who classmates said had been found to have a type of autism, was faring poorly and being bullied in high school. More recently, he had cocooned himself in front of electronic game consoles in the basement of their home, playing warfare games.

The contents of the Lanza house are of intense interest because the lives of the family have been picked apart since the shootings, often yielding little insight. A clear understanding of Adam Lanza’s thinking and the texture of his relationship with his mother and others has yet to emerge. What pushed him to his brutality may never be discovered.

After killing his mother at their home on the morning of Dec. 14, Mr. Lanza drove to the grade school that he once attended and carried out the massacre in less than five minutes, according to the search warrant.

The rampage brought the nation and the world to tears and touched off a continuing national debate over gun control.

Stephen J. Sedensky III, the state’s attorney who is in charge of the investigation, said in a statement on Thursday that Mr. Lanza shot his mother in the forehead with a .22-caliber rifle while she was in bed in her second-story bedroom.

At the school, he used a Bushmaster XM15-E2S semiautomatic rifle to fire 154 shots, the statement said. The police also found 10 30-round magazines for the gun, many of them partly or fully emptied.

Mr. Lanza also carried two semiautomatic handguns, one of which he used to kill himself. The police found a 12-gauge shotgun in the car he drove to the school.

The inventories attached to the warrants delineated pertinent items found by police in the home that Mr. Lanza shared with his mother, a two-story house with dark green shutters at 36 Yogananda Street in Newtown. Ms. Lanza was a gun enthusiast who often took her son to shooting ranges. She was divorced from his father, Peter Lanza, a General Electric executive.

The items included more than 1,600 rounds of ammunition bullets, some of them housed in a Planters peanut can and a Nike shoe box, and an array of weapons found in a brown safe and in bedroom closets. The lists mention four guns, including the shotgun found in the black Honda Civic that Mr. Lanza drove to Sandy Hook, and 70 shotgun shells found in the car. There were two rifles, including the one used to kill Nancy Lanza, as well as a BB gun and a starter pistol.

The police also found a certificate from the National Rifle Association bearing the name Adam Lanza. The type of certificate was not clear. The organization said on Thursday that Adam Lanza and Nancy Lanza were not members.

There was also a receipt from a shooting range in Oklahoma, an N.R.A. guide to the basics of pistol shooting and training manuals on the use of a variety of firearms, including a Bushmaster.

Photo

Adam LanzaCredit
NBC News, via Associated Press

There were paper and cardboard gun targets, as well as a considerable amount of computer equipment and game consoles and equipment. There was a hard drive that appeared to have been deliberately smashed.

There were numerous books connected to autism. One was titled, “Born on a Blue Day — Inside the Mind of an Autistic Savant.”

Classmates of Mr. Lanza and others who knew the family have said he had an autism variant known as Asperger’s syndrome, though investigators have never confirmed that diagnosis. Even so, his association with the disorder has raised alarms among parents of children with the diagnosis, who have expressed concerns that the public might believe that those with autism are prone to violence.

Experts say people with autism spectrum disorders are often bullied in school and the workplace and frequently suffer from depression, anxiety and suicidal thoughts. But the experts also say there is no evidence that they are more inclined than any other group to commit violent crimes.

Though Mr. Lanza’s life remains mostly opaque, interviews in recent weeks show that he was a socially fragile individual captivated by warfare video games and bent on military service.

Marvin LaFontaine, 53, a mechanical engineer who considered himself a friend of Nancy Lanza from Kingston, N.H., where Ms. Lanza grew up, kept in touch with her chiefly by e-mail, Facebook and phone until 2010. He remembered that Adam Lanza deeply admired one of his mother’s brothers, a retired Kingston police officer named James Champion. Mr. LaFontaine said Mr. Lanza was keen on joining the military, as his uncle, Mr. Champion, had done.

“This all started when Adam was 3 or 4, and became more ingrained as Adam got older and ultimately decided that he wanted to become a Marine,” Mr. LaFontaine said.

Classmates said Mr. Lanza was smart but acutely shy, and was not known to have close friends. His mother frequently moved him in and out of school, and at times home-schooled him. Several years ago, when Mr. Lanza was in high school, Mr. LaFontaine said Ms. Lanza shared with him that “the problems with Adam were getting worse and that he was getting picked on and bullied and was starting to shut down.”

A Newtown rabbi who counseled the families of victims of the shooting said former classmates of Mr. Lanza had told him that Mr. Lanza was sometimes the object of ridicule in high school. Other classmates have said they did not recall instances of his being bullied.

Mr. LaFontaine said Ms. Lanza had been weighing a number of options, which included once again removing him from school, which she later did. Mr. Lanza left Newtown High School after 10th grade. For a time, he attended college.

Despite his issues, Mr. LaFontaine recalled, “Nancy was generally confident that he could beat this and grow up into a normal, confident man, and that she could help him to do that.”

He shared an e-mail in which she described how much she enjoyed living in Newtown, which is about 75 miles northeast of Times Square.

“People are so nice here,” she wrote. “I feel very lucky to have found a place where there is such a feeling of community.”

While the documents show that Mr. Lanza readily had access to weapons, a fact that was already known, by themselves they do not shed light on his motives, said Jack Levin, a professor of sociology and criminology at Northeastern University who has written several books on mass murders.

But in many school shootings, the killers were often bullied or ostracized by their classmates, “and the motive is revenge,” Mr. Levin said in a telephone interview.

And Mr. Lanza did have other traits in common with school gunmen, including social isolation and access to weapons and firearms training, Mr. Levin said. The clipping on the Northern Illinois shooting, Mr. Levin said, indicates that, like some mass murderers, he might have been inspired by past shootings.

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Nancy Lanza on a cruise in Newport Harbor in 2008.Credit
Reuters

Adam Lanza had cut off contact with his father and his older brother, Ryan Lanza, in recent years, according to various accounts.

David Burton, a former co-worker of Peter Lanza’s at General Electric who is now a lawyer in private practice, said Peter Lanza spoke rarely about Adam Lanza’s challenges.

Still, Mr. Burton recalled being at a Christmas party in 2010 or 2011 at which Peter Lanza’s eyes lit up upon learning that Mr. Burton’s wife was an educational consultant.

Peter Lanza peppered her with questions, Mr. Burton said.

“When Peter learned of her expertise, he brought up Adam to her, and was clearly looking for an educational solution for Adam,” Mr. Burton said. “She mentioned some boarding school options. It’s one of those things you look back and say we should’ve done more there. But then everybody gets busy and it doesn’t happen.”

Two law-enforcement officials who were initially involved in the investigation said in recent interviews that the Newtown police had never been called to the Lanza home for any disturbances, and that before the shootings the family was basically unknown to the authorities.

They said they believed that Mr. Lanza had spent most of his time in the basement of the home, primarily playing a warfare video game, “Call of Duty.” According to these officials, it also appeared that Mr. Lanza may have taken target practice in the basement.

In the documents released on Thursday, prosecutors redacted the names of witnesses interviewed by the police, but shared some of what they said.

The day of the shooting, agents from the Federal Bureau of Investigation interviewed a person who said Mr. Lanza rarely left his home. The witness considered Mr. Lanza to be a “shut-in and an avid gamer who plays ‘Call of Duty,’ amongst other games,” according to a law-enforcement affidavit accompanying the warrants. It also said the witness told agents “that school was Adam’s ‘life,’ ” referring to Sandy Hook Elementary School, which Adam Lanza had attended.

Additional material turned up in the searches might contain clues into Mr. Lanza’s thoughts in the days and weeks before the massacre, but their contents were not divulged. Police officers found seven journals written by Mr. Lanza, along with several of his drawings. The drawings were not described.

Beside three photographs of what appears to be a corpse, there was an article from The New York Times in February 2008, about a shooting at Northern Illinois University in DeKalb, Ill. In that shooting, Steven Kazmierczak killed 5 people and injured 21 on Valentine’s Day before he killed himself.

Whatever problems Adam Lanza may have had, the documents indicate that Nancy Lanza was comfortable with his being around guns.

The holiday card to Mr. Lanza from his mother contained a check that specified that the money was to buy a “C183 (Firearm),” the documents say.

The date and amount of the check are not listed. It was not clear if the reference to C183 contained a typographical error and was intended to mean a CZ83, which is a semiautomatic handgun.

The Hartford Courant previously reported that investigators had found news articles about the Norwegian mass murderer Anders Behring Breivik in a bedroom of Mr. Lanza’s. Mr. Breivik killed 77 people in two attacks in July 2011, most of them teenagers who were attending a summer camp.

Those articles were not mentioned in the documents released on Thursday.

The searches did turn up medical records, which are not identified, as well as some of Mr. Lanza’s school records.

A version of this article appears in print on March 29, 2013, on page A1 of the New York edition with the headline: Newtown Killer’s Obsessions, in Chilling Detail. Order Reprints|Today's Paper|Subscribe